The present invention relates to an apparatus for preventing any interior contamination of an air-turbine hand-piece and its drive mechanism -or dental treatment such as cutting a tooth.
Conventionally, in practically available air-turbine hand-pieces for dental treatment, a high-pressure (2 to 4 kg/cm.sup.2) air jet from an external pressurized air supply source is applied, via a supply pipe, on air-receiving blades of an air-turbine mounted on an end of the hand-piece, and is discharged from a discharge pipe; the air-turbine is thereby rotated at high speed (about 400,000 r.p.m.) to drive a cutting tool directly connected to the air-turbine.
Also, in order to prevent the cutting tool from developing heat and to wash away the chips of a tooth while the hand-piece is in use, cooled water jet is applied from an external water supply source to a blade tip of the cutting tool via a water pipe, and a tip air nozzle is juxtaposed to the discharge end of the water pipe for jetting an air stream to vaporize the cooled water.
In the hand-piece in which the cutting tool is rotating at high speed, in order to avoid the risk of contacting the inside skin of a mouth when the cutting tool is removed out of the mouth upon termination of the treatment of the interior of the mouth, it has been a common practice to discontinue supplying air to the airturbine to thereby stop rotation of the cutting tool at a working position.
However, after the supply of air to the airturbine rotating at high speed is stopped, the air-receiving blades continues rotating by inertia for a while, and therefore, a phenomenon causing a negative pressure occurs in the interior of the hand-piece.
As a result, at the tip of hand-piece assuming the working position, the cooled water attached to a chuck portion of the cutting tool and other parts is sucked into the structure of the hand-piece as dirty water containing the chips of a tooth, saliva, blood, various germs, etc, thus causing a contamination of the interior of the hand-piece.
This interior contamination due to the negative pressure phenomenon extends to a supply pipe connected to the hand-piece, to a discharge pipe, to a chip air pipe, and to a water pouring pipe. Further, the contamination occasionally extends to the mechanism for controlling the supply and discharge of air or water through these pipes.
Consequently, though only the airturbine at the tip of the hand-piece is removed from the mechanism after completion of the treatment and is then disinfected, the interior of the airturbine can be contaminated again from the air and water supply side as air and water are supplied to the hand-piece via the individual pipes for the next treatment, thus making the previous disinfection of the turbine wasteful.
Under these circumstances, only the effective disinfection of this kind of hand-piece is to prevent the interior of the hand-piece from being contaminated.
To this end, the most suitable measure for preventing this contamination of the interior of the hand-piece is to maintain the interior of the hand-piece at positive pressure so as to keep various germs from entering into the interior of the hand-piece from outside.
Most of existing modern dental treatment chairs are furnished with various tools as well as the drive mechanism for the airturbine hand-piece. Since these furnished tools are arranged in order and united in a compact form so as to facilitate the treatment, it is very difficult to additionally furnish on the chair a control mechanism composed of several air and electromagnetic valves which keeps the interior of the hand-piece a positive pressure after completion of the treatment.
Therefore, this kind of mechanism must be minimized both in size and in weight, or it cannot be practically useful.
With the foregoing problems in view, the present inventor developed a practically useful apparatus (Japanese Utility Model Application No. 146230/1987) which prevents the interior of airturbine hand-piece from being contaminated and with which various functions required to this kind of apparatus can be accomplished.
An air change-over circuit unit for supplying the pressurized air (0.1 to 0.3 kg/cm.sup.2) required to keep the interior of the hand-piece at positive pressure, when the supply of the pressurized air of 2 to 4 kg/cm.sup.2 pressure required to operate the hand-piece is stopped, must be operable to shift individually at least three system circuits, namely, an air supply circuit, an air discharge circuit and a chip air circuit. As a consequence, if this change-over circuit unit was composed of conventional ordinary air valves or three-direction valves, it would have been a complex passageway assembly.
Therefore, in the above-mentioned apparatus developed by the present invention, since conventional ordinary valves are used, the passageways are complicated so that the block body is required to be provided with many longitudinal and transverse passageways. Further, the passageways must be arranged in high density in the block body as it is desired to make the entire size of the apparatus compact, and for this reason, such complex passageways assembly must be manufactured carefully with high-degree perforation technology. Furthermore, the assembly must be manufactured by using as material a metal that is easy to process.
However, metal materials can be easily oxidated. Assuming that the hand-piece is dipped in a sterilization liquid for a long period of time due to the failure of switching on a low-pressure air to keep the interior of the hand-piece at a constant pressure, the sterilization liquid fills in the interior of the hand-piece and occasionally flows reversely through the air pipe to reach the block body.
In the sterilization liquid in this case, sodium hypozinc acid which is strong in oxidation to metal, is occasionally used so that rust develops in the passageways in the block body as well as in the air valve. This rust would impede the operation of the tools.